1. Field of the Invention
The present invention relates in general to an ink-jet printer.
2. Discussion of Related Art
Generally, in an ink-jet printer wherein a carriage which carries a recording head reciprocates, it is known that an accuracy with which ink droplets ejected from the recording head attach to target or intended positions on a recording medium such as a sheet of paper is largely influenced by not only ejection-related conditions such as an accuracy with which nozzle holes are formed and a water-repellent property of a nozzle surface of the recording head in which the nozzle holes are formed, but also flying conditions under which the ink droplets fly from the recording head to the recording medium. Namely, it is known that the ink droplets ejected from the recording head are subjected, during flying toward the recording medium, to air flows (cross winds) caused as a result of the reciprocating movement of the carriage on which the recording head is mounted.
Where there is a variation in the degree of influence of the air flows among the ink droplets ejected from the respective nozzle holes, actual attaching positions on the recording medium to which the respective ink droplets actually attach deviate from target attaching positions on the recording medium to which the respective ink droplets should attach. In bi-directional printing, this causes bi-directional deviation in the attaching position of the ink droplet, resulting in a deterioration in the printing quality.
Particularly, in the light of the recent trend toward high-speed operation of the carriage as well as downsizing of the ink-jet printer, the moving speed of the carriage is increased to a level ranging from about 75 cm/s to about 100 cm/s. Therefore, the air flows generated by the reciprocating movement of the carriage give a significantly large influence on the flying of the ink droplets from the recording head toward the recording medium.
Described more specifically, the ink-jet printer has a structure shown in FIGS. 3-5, for instance. The ink-jet printer generally indicated at 101 includes a casing 102 consisting of an upper casing member 102A and a lower casing member 102B. The casing 102 defines a closed interior space which is inhibited from communicating with an outside. In the interior space of the casing 102, a head unit 103 is disposed so as to be reciprocally movable, relative to a recording medium P, by driving means (not shown) in a rightward and leftward (transverse) direction of the printer indicated by an arrow A in FIG. 3 along a guide portion 104A supported by a frame 104, so that images, characters, and the like are recorded on the recording medium P. The head unit 103 includes a carriage 103A and a recording head 103B mounted on the carriage 103A. Ink droplets are ejected from a plurality of nozzle holes of the recording head 103B for performing printing on the recording medium P placed on a platen 105. The frame 104 also supports a sheet feed roller 106 and a sheet-discharge roller 107 such that these rollers 106, 107 are rotatable. In the following description, the direction in which the head unit 103, accordingly the carriage 103A moves may be referred to as a “carriage-moving direction”.
In the thus constructed ink-jet printer 101, for the purpose of downsizing the printer 101, a clearance S1 (FIG. 3) between a spatial region defined by the movement of the head unit 103 and an upper portion of the casing 102, in other words, between an upper surface of the carriage 103A and the upper portion of the casing 102, is made as small as a clearance S2 (FIG. 3) between a nozzle surface of the recording head 103B in which the nozzle holes are formed and the recording medium P. In this arrangement, the above-described air flows caused as a result of the movement of the carriage 103A and entered the clearance S1 are not likely to pass through the clearance S1.
In the meantime, clearances S3, S4 (FIG. 4) between respective side surfaces of the carriage 103A which are opposed to each other in a perpendicular direction that is perpendicular to the carriage-moving direction in plan view and portions of the casing 102 which are respectively opposed to the respective side surfaces of the carriage 103A are larger than the above-described clearance S1 between the upper surface of the carriage 103A and the upper portion of the casing 102. Therefore, the air flows generated by the movement of the carriage 103A and entered the clearance S1 are likely to flow toward the clearances S3, S4 as shown in FIG. 6A. Accordingly, the ink droplets ejected from the nozzle holes in the neighborhood of the clearances S3, S4 are influenced by the air flows more largely than the ink droplets ejected from the other nozzle holes, causing deviation (disturbance) in the attaching positions of the respective ink droplets ejected from the nozzle holes in the neighborhood of the clearances S3, S4. In other words, the deviation of the attaching positions of the ink droplets ejected from the opposite end portions of the recording head 103B as seen in the perpendicular direction (in the neighborhood of the clearances S3, S4) becomes larger than the deviation of the attaching positions of the ink droplets ejected from a middle portion of the recording head 103B as seen in the perpendicular direction.
Described more specifically, under ink-ejection conditions in which, upon ejection of the ink droplets, small-sized ink particles (hereinafter may be referred to as “satellite particles”) are ejected together with main ink particles, there are recorded, on the recording medium, dots U2 formed by attachment of the satellite particles, in addition to dots U1 formed by attachment of the main particles, as shown in FIG. 6B. In this instance, because the satellite particles are lightweight, the satellite particles ejected from the opposite end portions of the recording head (in the neighborhood of the clearances S3, S4) as seen in the perpendicular direction are largely influenced by the air flows flowing from the clearance S1 toward the clearances S3, S4, so that the attaching positions of those satellite particles largely deviate from the target attaching positions. In other words, since air flows flowing on the recording medium in the vicinity of the clearances S3, S4 flow or escape outwards and upwards through the clearances S3, S4, the lightweight satellite particles are influenced by such air flows and undesirably fly in directions inclined with respect to a direction in which the main particles fly. The dots U2 formed by attachment of the satellite particles nearer to the clearances S3, S4 tend to largely deviate in directions inclined with respect to the dots U1 formed by attachment of the corresponding main particles.
Where the casing 102 has the closed structure which inhibits communication with the outside, the above-indicated air flows generated by the reciprocating movement of the carriage 103A hardly escape or leak from the casing 102. Therefore, it is conceivable that the above-indicated tendency becomes larger, namely, the influence of the above-indicated air flows on the flying of the ink droplets becomes larger.
In an attempt to prevent the deterioration in the print quality due to the air flows generated as a result of the reciprocating movement of the head unit (the carriage), it is proposed in U.S. Pat. No. 6,561,620 corresponding to JP-A-2002-361858, for instance, to provide a skirt member which extends from the carriage in the carriage-moving direction so as to be substantially parallel with the nozzle surface of the recording head.